1. Field of the Invention
The present invention relates to wireless data communication. More particularly, the present invention relates to a wireless data communication apparatus and method using a multicarrier and to a transmission frame format therefor.
2. Description of the Related Art
In wireless data communication using burst data, the efficient use of system resources often requires that resources be allotted and retrieved dynamically. In a conventional centralized wireless data system, transmission frames are usually classified by the broadcast period, the downlink period, the uplink period, and the contention period. In such a system, information regarding how to manage the downlink period, uplink period and contention period is contained in the broadcast period. In general, in a centralized wireless data system, each station requests the allocation of resources from a net access group switching center through a contention method or a piggyback method. In the former case, stations transmit a message requesting the allocation of resources to the net access group switching center during the same contention period. Such a process suggests that there is a high probability that several stations request the allocation of resources at the same time, which would cause contention in the request for the allocation of resources. In the latter case, a station that desires to transmit data requests the allocation of resources in a next transmission frame using a specific head field included in the resources it has already been allocated. Thus, there is less contention in the request for the allocation of resources in the piggyback method than in the contention method.
In a station that desires to transmit burst data to a net access group switching center, the request of resources through a contention method takes place at the start of the data burst transmission. The request through a piggyback method, on the other hand, is performed continuously during the transmission. Even though contention may be minimized in many ways, there still are numerous obstacles in enhancing the quality of various data services, such as real-time data services, when requesting resources using the contention method.
To solve this problem, contention resolution methods such as slotted-aloha methods are adopted. According to the slotted-aloha method, each station, which is to request resources in a contention period having M time slots, generates random values from 1 to M-1 and delays a time slot to correspond to the generated value, thereby minimizing the occurrence probability of the contention in the request for resources. In the slotted-aloha method, the occurrence probability of the contention can be reduced by increasing the length of the contention period, but this poses more difficulties in the effective use of resources.
According to a method of solving the problem of the slotted-aloha method, resources are requested by allocating one sub-carrier for each station and polling a sub-carrier allocated in a predetermined period. In this method, the sub-carrier allocated for each frame is hopped to overcome multi-path fading. However, in the event that a specific sub-carrier is lost due to the multi-path fading, resources must be requested in a next frame, and therefore, this method is not adequate for the request for resources at high speed.